Wow, color me surprised then about that it's actually a new beer. I did not expect breweries would do something of that (small) scale.
Something else to consider is that it's profitable exposure for the brewery. They're going to make seasonal batches anyway, and now fans of some rock band they've never heard of will be searching out six-packs of it. I'd say that they're better off letting somebody with some name recognition design their beer than simply trying to come up with something original on their own hoping for the random shopper to maybe give it a shot. Besides, some of these people actually have good taste in beer.
Personally, I think it's an interesting way to connect with some of these people. Arry and Bruce put a whole lot of effort into Trooper to make it exactly the beer they'd want to drink. Personally, I think it sucks, but it's really cool to know what their personalized beer is like. I've never been a fan of Dave Mustaine, but I sure like his beer. I just find it interesting to gain an understanding of what these folks dig.